Vibration analysis in different perspectives

July 8, 2022
Vibration analysis in different perspectives

Today there are different ways to collect and analyze vibration in rotating equipment. This is not news, what we want to bring up is the reliability and assertiveness of the ways of measuring vibration.

There is a mistrust between an offline and an online measurement with wired sensors versus wireless sensors also with online or offline measurements.

Our proposal is to demystify this paradigm and prove that there is compatibility between vibration levels, their frequencies, and also to highlight the aspects and forms that add to the analyst’s confidence in applying his diagnosis.  

At Vale’s Serra Norte Plant, through the Predictive Inspection report, it was possible to put into practice the comparison proposal between collections with wired and wireless sensors. In this opportunity we detected a series of failures of mechanical looseness in a Hydrodynamic Seal Pump. 

COMPARISON: WIRED VERSUS WIRELESS SYSTEM  

Analyzing the Hydrodynamic Seal Pump at the Serra Norte Power Plant, using both the wired and wireless systems, it can be observed through the collection the spectrum in velocity (mm/s) with the presence of harmonics of the RPM at point 3 of the pump.

Below there is a comparison between Figures 1 (a) and (b), which represent the spectra showing the amplitudes and harmonics at the highest excitation frequency for the 178Hz frequency that comes from the blade passage, as well as the frequency related to the elastic element of the high rotation coupling.  

Figura 1.(a)

Figura 1.(b)

  

For comparison and confirmation of the diagnosis of looseness followed by a misalignment there is the autocorrelation analysis tool of the wired and wireless systems figures 2 (a) and (b). 

Figura 2.(a)
Figura 2.(b)

Below there are the trends of the global values Fig. 03 (a) (b) that provide early detection of an anomaly. One can evaluate the evolution of the failure in both ways of measuring. It’s important to note the importance of a triaxial system, because it makes it possible to monitor the machine’s response in all three directions without increasing the collection time compared to a uniaxial sensor. Another essential characteristic is to be able to reconcile physical aspects of the system with the high number of samples, that is, as it is well known, the machines suffer various process, weather, and human interferences. So the higher the collection frequency, the more possibility to visualize any machine changes.  

Figura 3.(a)
Figura 3.(b.1)
Figura 3.(b.2)

RESULT ANALYSIS AFTER EQUIPMENT REPAIR USING THE DYNAPREDICT SOLUTION

The differential of the DynaPredict Solution is to have analysis and diagnosis tools that show before and after the mechanical intervention, pointing out what resulted in the change of the elastic element and the alignment of the motor and pump assembly. 

Envelope technique (before / after) 

Waveform envelope (before / after)

Circular Waveform of the Autocorrelation (before / after) referring to the elastic element with wear of the high speed coupling. 

Spectrum at speed (before /after) 

Linear waveform (before / after)

Cepstrum Technique (before/after)  

Continuous Trend (before /after)

3D waterfall (before/after)   

DYNAPREDICT DIFFERENTIAL IN VIBRATION

Dynamox offers a continuous monitoring system. The data obtained by the dataloggers are stored in the cloud and analyzed by the algorithms of the DynaPredict Platform that issues alerts (A2) when the asset reaches critical levels, alerting to the severity of the operating conditions of the monitored assets via email. Another key point of the wireless system is the possibility of removing men from risky places, increasing safety in the work environment.  

We highlight the fact that there is no need to invest in large infrastructures for the implementation of the continuous monitoring system, bringing a reduction in operating costs. Finally, the possibility of sensors being installed in places of difficult access brings advantages in asset monitoring.

RELIABILITY, PREDICTABILITY AND ASSERTIVENESS: ADVANTAGES OF THE DYNAPREDICT SOLUTION

The DynaPredict Solution offers a robust system full of tools that count on periodic updates, so the decision making and maintenance planning happens in a more predictable and assertive way, enabling reliability, integrity, and performance of industrial assets.  

By relying on a triaxial continuous monitoring system, the amount of samples collected by Dynaloggers is much higher than the conventional off-line monitoring systems, which depend directly on the technicians’ measurement availability. The monitoring solution offered by Dynamox counts on automatic measurements in intervals from 1 to 60 minutes. An example would be a parameterization of collection every 30 minutes, totaling 432 samples per day.  

As we can see, vibration measurement with wired sensors (offline) and wireless sensors showed equivalence in amplitude and frequency, so we can demystify the misinterpretations. In the world of predictive maintenance it is important to obtain an adequate system, which enables detection and analysis tools so that the decision making is always assertive.   

Learn more about the features of the DynaPredict Solution.


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